Abstract:Harmonics can be applied to the phase current and back EMFs of multi-phase motors to improve the torque output capability, but this increase is only applicable when the harmonic order is lower than the seventh order. Compared with the fifth harmonic and the seventh harmonic injection, the third harmonic injection can effectively improve the output torque of the dual three-phase permanent magnet motor without generating torque ripple. In this paper, a theoretical analysis of the phase current and back-EMF injection of the third harmonic to increase the output torque of the dual three-phase motor is carried out. The drive system is improved by connecting the two isolated neutral points of each set of windings to different midpoints of the capacitor to provide a flow path for the third harmonic current to balance the current between the two sets of windings. A new permanent magnet shaping method is proposed, which takes into account the stator cogging effect, iron core saturation, and magnetic leakage between tooth tips and poles, and obtains the optimal quasi-sinusoidal back EMF. The optimal quasi-sinusoidal current interacts with the optimal quasi-sinusoidal back EMF, and the output torque of the motor is increased by 18.2% under the condition of constant torque ripple. Finally, the correctness of the theoretical derivation is verified through finite element analysis and experiments.